The present invention relates to a substrate processing apparatus for coating resist onto a substrate such as a semiconductor wafer and an LCD substrate (liquid crystal display) and developing the resist-coated film pattern-exposed.
In a photolithographic process for manufacturing a semiconductor device and an LCD, a substrate is coated with resist, exposed to light and developed. The series of processes as mentioned is usually carried out by using a substrate processing apparatus. The substrate processing apparatus has a plurality of heating units including a preliminary heating unit and a dry unit. Each of the heating units has a hot plate installed therein.
The hot plate has a built-in electrical resistance heater, which generates heat when current is supplied thereto. To warm up a hot plate, which is cold at the time the apparatus is started up, to a required temperature, it takes about several to ten minutes after power supply is started. However, to stabilize the temperature of the hot plate, approximately 30 minutes is required after the initiation of the power supply. During the start-up period in which a cold hot-plate is warmed up to a predetermined temperature, a large power consumption is required, whereas in the stable condition after the hot plate reaches the predetermined temperature, power is supplied intermittently. Hence, required power consumption is a reactively low.
In the processing apparatus, i.e., a coating/developing apparatus, a wafer W is loaded into processing units in a predetermined order. The wafers are loaded into each of the processing units one by one in accordance with the predetermined order. Therefore, it may be sufficient if each processing unit is warmed up to the stable state by the time the wafer W is loaded therein.
However, in a conventional coating and developing apparatus, power is supplied to each of the built-in heaters of a plurality of processing units simultaneously at the time the apparatus is started up. Hence, a large amount of power is consumed at the start-up time. In this connection, electric parts having a large capacity (tolerance) must be used in a power supply cable and a breaker, etc. As a result, the manufacturing cost of the apparatus inevitably increases. Since the power supply cable and the breaker must have a capacity nearly 4 times larger than the power-consumption at a normal operation time, the breaker may not properly work if a large power is consumed when abnormality accidentally takes place during the normal operation time, failing in security control.